This invention relates to the field of polyether active hydrogen compounds. More particularly, the invention relates to polyether compounds having at least two terminal active hydrogen groups, and preparation thereof.
An active hydrogen group is a functional group which will react with an isocyanate group. Polyfunctional compounds having active hydrogen groups are used, for instance, in the preparation of polyurethanes, which are polymers useful in producing foams, molded plastics and the like. The Zerewitinoff test described by Kohler in the Journal of the American Chemical Society, Vol. 49, page 3181 (1927) predicts the tendency of a hydrogen-containing group to react with isocyanates. Active hydrogen group-containing compounds include amines, alcohols, thiols, carboxylic acids, carboxamides and the like.
A polyether active hydrogen compound is a compound having more than one ether group as well as at least one active hydrogen group. Polyhydroxy polyethers are referred to as polyether polyols. Polyether compounds are commonly prepared by the catalyzed addition of an alkylene oxide, a sequence of alkylene oxides or a mixture of alkylene oxides to an organic initiator compound advantageously having at least two active hydrogen atoms. Such addition of alkylene oxides is referred to as alkoxylation. An alkoxylation catalyst may be alkaline, neutral or acid. In a commercial operation, the usual catalysts are either sodium hydroxide or potassium hydroxide. The use of catalysts which are the reaction product of a porphyrin compound and an organoaluminum compound is also known for production of polyether polyols as described in U.S. Pat. No. 4,654,417.
Whatever the catalyst used to prepare polyether polyols from alkylene oxides, alkylene oxides having one or more alkyl substituents, such as propylene oxide, butylene oxide, and the like, show a strong tendency to react with active hydrogen compounds at the least substituted carbon of the epoxy ring, such that terminal secondary or tertiary hydroxyl groups are formed. Primary hydroxyl groups are, however, more reactive with isocyanate groups than are secondary and tertiary hydroxyl groups. Compounds having primary hydroxyl groups are, therefore, generally preferred for preparation of polyurethanes, when fast reaction is desirable, for instance in preparing molded polyurethanes, particularly reaction injection molded (RIM) polyurethanes.
Ethylene oxide is often used to produce primary hydroxyl groups in the form of terminal hydroxyethoxy groups. Ethoxy groups in a polyether polyol generally increase a molecule's tendency to absorb water, e.g. moisture from the air. Polyurethanes formed from polyols having ethoxy units often absorb enough water, e.g. from humid air, to change the physical properties of a polyurethane. For instance, a polyurethane foam that absorbs moisture generally becomes soft, and may swell and demonstrate reduced load-bearing properties. High levels of ethylene oxide repeating units may also cause a polyether to be more crystalline.
One way to avoid the problems of water absorption of poly(ethylene oxide)-containing polyols, yet have terminal primary hydroxyl groups, is to form a polyether from alkylene oxides other than ethylene oxide and cap that polyether with at least one ethylene oxide unit as described, for instance, in U.S. Pat. Nos. 3,336,242; 3,776,862; 4,195,167; 4,421,872; 4,299,993; and 4,440,705. Because a polyether polyol having a primary hydroxyl group is more reactive with ethylene oxide than is a secondary or tertiary hydroxyl group, ethylene oxide molecules tend to add preferentially to molecules already having hydroxyethoxy groups rather than adding to polyethers having secondary or tertiary hydroxyl groups. Thus, the product of capping polyethers with ethylene oxide is generally a mixture of polyethers having one or more polyethoxy terminal segments with some of the polyethers having one or more terminal segments without hydroxyethoxy groups, thus, without primary hydroxyl groups. For instance, in a process for ethylene oxide capping of a poly(propylene oxide) polyol, wherein about 3 percent potassium hydroxide is used as catalyst and a polyol having an equivalent weight of approximately 2000 is produced, those skilled in the art would expect that capping about 70-80% of the poly(propylene oxide) chains would require use of about 15-20% by weight ethylene oxide based on total alkylene oxides. Capping of 80-85% of the poly(propylene oxide) chains would require that about 20-25 % by weight of the alkylene oxide be ethylene oxide. For purposes of the foregoing discussion, a polymer chain is that portion of a polyether polyol molecule initiated at one active hydrogen group of an initiator and terminated by a hydroxyl group.
It would be useful to prepare polyether compounds having active hydrogen groups on primary carbon atoms without ethylene oxide capping.